Are you sure your patient has catheter-acquired urinary tract infection? What should you expect to find?

Catheter-acquired urinary tract infection (UTI) is one of the most common health care acquired infection. Acquisition of new bacteriuria while a catheter remains in situ is 3 to 7% each day.

An indwelling catheter is considered short term when in situ less than 4 weeks; if longer than 4 weeks, it is a long-term (chronic) indwelling catheter.

Antimicrobial treatment is not indicated for asymptomatic patients with catheter-acquired urinary tract infection, except prior to an invasive urologic procedure. Screening of patients with indwelling catheters to identify bacteriuria is also not recommended, except prior to an invasive urologic procedure.

The most common clinical presentation of symptomatic catheter-acquired urinary infection is fever alone. Severe presentations with bacteremia, severe sepsis, or septic shock occur in only a few patients.

The most effective preventive strategy is to limit catheter use to patients with clear indications and, when a catheter is used, to remove the device as soon as possible.

Most patients with catheter-acquired urinary infection are asymptomatic and identified only if a positive urine culture is reported.

The most common symptomatic presentation when a catheter is in situ is fever without localizing findings. Thus, the diagnosis is usually a diagnosis of exclusion.

Localizing signs or symptoms that may be present include suprapubic pain or tenderness, costovertebral angle pain or tenderness, catheter obstruction, or acute hematuria.

If fever develops in a bacteriuric patient in the clinical context of recent (less than 24 hours) onset of hematuria, catheter obstruction, or catheter trauma and there is no alternate source, UTI is highly likely.

Spinal-cord injured patients with a high level cord injury may present with autonomic dysreflexia.

Symptomatic infection may develop after catheter removal. When this occurs, the clinical presentation is similar to that in patients without indwelling catheters who present with symptoms of acute upper tract (renal) or lower tract (bladder) infection.

How did this catheterized patient develop urinary tract infection? What was the primary source from which the infection spread?

Infection in individuals with an indwelling catheter is usually a result of biofilm formation along the catheter that ascends into the bladder along both the internal and external catheter surfaces.

Biofilm formation is universal on indwelling catheters. It is initiated immediately following catheter insertion; most catheterized patients have bladder bacteriuria by 14 days following catheter insertion.

Biofilm is a complex material of bacterial and/or yeast aggregates that grow in an exopolysaccharide material produced by the organisms. Magnesium and calcium ions, Tamm–Horsfall protein, and other urine components are incorporated into the biofilm.

These bacteria and yeast originate from the periurethral flora or following contamination of the catheter, tubing, or drainage bag when there are breaks in the closed drainage system.

Less common ways for acquisition of bacteriuria include introduction of bacteria directly into the bladder at the time of catheter insertion or reflux of infected urine from the drainage bag or tubing into the bladder when there is inappropriate catheter management.

Organisms carried on the hands of staff members or on shared equipment, such as urine volume measuring containers, may be a source for infecting organisms if they contaminate the drainage bag or tubing.

Which individuals are at greater risk of developing a catheter-acquired urinary tract infection?

The duration of catheterization is the most important determinant of bacteriuria.

Patients with chronic indwelling catheters always have bacteriuria or funguria, usually with multiple organisms.

The predictors of symptomatic infection, rather than bacteriuria, are not well studied. Trauma to the catheter with mucosal bleeding and catheter obstruction are recognized predisposing events, but precipitate infection for only a small proportion of symptomatic patients.

Beware: there are other diseases that can mimic catheter-acquired urinary tract infection:

Fever in a bacteriuric patient with an indwelling catheter and without localizing genitourinary signs or symptoms may originate from many sources other than the urinary tract. In the absence of localizing genitourinary findings, alternate diagnoses should always be considered.

What laboratory studies should you order and what should you expect to find?

Results consistent with the diagnosis

A urine specimen for culture with a quantitative count greater than 105 CFU/mL of one or more organisms is consistent with the diagnosis. However, although a positive urine culture is essential for a diagnosis of urinary infection, it does not confirm symptomatic infection.

Symptomatic infection may occur with quantitative counts of less than 105 CFU/mL, but this is uncommon. When a lower quantitative count of organisms is isolated, the diagnosis of symptomatic urinary infection should be reconsidered.

The urine specimen must be collected using a method that minimizes contamination.

For patients with a short-term (less than 2 weeks) indwelling catheter, the urine specimen should be collected by aspiration of urine through the sampling port or tubing.

When a chronic indwelling catheter has remained in situ for 2 weeks or longer, the catheter should be removed and replaced by a new catheter, then a urine specimen for culture should be collected through the replacement catheter prior to institution of antimicrobial therapy. The catheter in situ is coated with biofilm; a urine specimen collected through this biofilm is contaminated with organisms growing in the biofilm and does not accurately represent bladder microbiology.

Patients with a short-term indwelling catheter usually have a single organism isolated; patients with a chronic indwelling catheter usually have two or more organisms isolated.

The urinalysis should be positive for pyuria, identified by either leukocyte esterase dipstick or microscopy. However, pyuria is a nonspecific finding that does not distinguish asymptomatic from symptomatic infection and may be attributable simply to the presence of the catheter without bacteriuria. Conversely, for a non-neutropenic patient, the absence of pyuria effectively excludes UTI.

The only diagnostic test that confirms symptomatic UTI is a positive blood culture with the same organism isolated from both blood and urine.

What imaging studies will be helpful in making or excluding the diagnosis of catheter-acquired urinary tract infection?

Imaging studies are not usually indicated for the diagnosis of catheter-acquired UTI.

Selected patients who fail to respond to appropriate antimicrobial therapy, who have frequent recurrent infections, or who have persistent hematuria should be investigated to exclude renal or bladder stones or other abnormalities, such as abscesses.

The optimal imaging technique is a contrast-enhanced computed tomography (CT) scan; noncontrast CT or ultrasonography may also be useful, depending on patient status and access to diagnostic testing.

What consult service or services would be helpful for making the diagnosis and assisting with treatment?

Consultation services are not usually required.

In selected cases with highly resistant organisms isolated or when the diagnosis is uncertain, infectious diseases or urology consultation should be considered.

If you decide the patient has catheter-acquired urinary tract infection, what therapies should you initiate immediately?

A urine culture must be obtained prior to initiation of antimicrobial therapy in every case to confirm the diagnosis and direct antimicrobial therapy.

Do not treat asymptomatic bacteriuria. Treatment of asymptomatic bacteriuria in residents with indwelling catheters has been identified as a frequent cause of inappropriate antimicrobial use.

Prophylactic antimicrobial therapy should be initiated only for bacteriuric patients prior to an invasive urologic procedure.

When symptomatic infection is diagnosed, reassess the indications for an indwelling catheter and discontinue the catheter, whenever possible.

When empiric antimicrobial therapy is initiated, considerations relevant to selection of the antimicrobial regimen include:

Review recent prior urine cultures from the patient, recent or current antimicrobial therapy, and consider the prevalence of resistance to potential infecting organisms in the facility for known or suspected susceptibilities of the likely infecting pathogens.

Review patient tolerance and renal function.

Parenteral therapy should be initiated for severe presentations, for patients who cannot tolerate oral therapy, or when organisms resistant to oral therapy are likely.

Empiric antimicrobial therapy should be reassessed when the urine culture becomes available, usually at 48-72 hours following initiation of therapy. Antimicrobial therapy should be modified based on antimicrobial susceptibilities of the organisms isolated. Initial parenteral antimicrobial therapy should be stepped down to oral therapy, where clinically possible.

If the catheter is to remain in situ, the shortest duration of treatment as possible is given. The optimal duration has not been defined in clinical trials, but, when there has been a prompt clinical response (afebrile by 48-72 hours), only 7 days therapy is recommended.

1. Anti-infective agents

If I am not sure what pathogen is causing the infection, what anti-infective should I order?

Figure 1.

Table IV.

If an indwelling catheter is still indicated and the current catheter has been in place for 2 weeks or longer, the catheter should be replaced prior to initiation of antimicrobial therapy.

Catheter replacement allows collection of a sample of bladder urine for culture that is not contaminated by catheter biofilm; organisms isolated are more relevant for therapeutic decisions.

Catheter replacement is associated with improved clinical outcomes, including a more rapid defervescence of fever and a decreased frequency of early symptomatic relapse following discontinuation of antimicrobial therapy.

What complications could arise as a consequence of catheter-acquired urinary tract infection?

Severe sepsis or septic shock may complicate infection in a few patients.

Patients with chronic indwelling catheters and infection with urease producing organisms, particularly Proteus mirabilis and Providencia stuartii, may develop crystalline biofilms leading to catheter obstruction or bladder or kidney stones.

Bacteremic infection may be followed by metastatic infection to other body sites. The skeletal system is most frequently involved, and the vertebral column is the single most common site. Endocarditis is the second most common metastatic infection.

What should you tell the family about the patient's prognosis?

Most patients will be afebrile by 72 hours following initiation of effective antimicrobial therapy.

The prognosis is excellent for patients with mild or moderate symptoms. Patients with severe presentations (i.e., septic shock) have a mortality of 10-20%.

As long as the urethral catheter remains in situ, the patient remains at increased risk for urinary infection.

What-if scenarios:

If there has not been substantial clinical response by 48-72 hours following initiation of empiric antimicrobial therapy:

The urine culture results should be reviewed to confirm the susceptibility of the infecting organism to the empiric antimicrobial therapy.

If the bacteria isolated is susceptible to the empiric regimen, potential diagnoses other than catheter-acquired UTI should be reconsidered.

If no alternate diagnosis is apparent, investigations for underlying genitourinary abnormalities, such as obstruction, abscesses, or emphysematous infection, should be considered.

Exceptionally, for patients with a chronic indwelling urethral catheter that cannot be removed and severe or very frequent recurrent infections, a suprapubic catheter or cystectomy with ileal conduit may be considered. However, the relative risks or benefits of these approaches for voiding management are not well described.

How do you contract catheter-acquired urinary tract infection and how frequent is this disease?

Detailed epidemiology

Acquisition of bladder bacteriuria occurs at a rate of 3-7% per day for patients while the indwelling urethral catheter remains in situ.

The daily rate of acquisition is higher for women, for patients with increased periurethral colonization with potential uropathogens, and if there have been breaks in the closed drainage system.

Patients receiving antimicrobial therapy have a lower incidence of bacteriuria during the first 4 days of catheterization, but subsequently experience the same daily risk as patients not receiving antibiotics, while organisms isolated have increased antimicrobial resistance.

In a prospective cohort study of 1497 acute care patients with a new short-term catheter insertion, fever, dysuria, urgency, or flank pain were identified as frequently in patients with as without bacteriuria. Only four episodes of bacteriuria (0.3% of catheters and 1.7% of bacteriuric catheters) had concordant blood and urine isolates, and only one of these four had no alternate potential source for bacteremia.

A prospective randomized clinical trial of two different catheters reported an incidence of 1.3-1.6 per 100 indwelling catheter days for symptomatic infection. Concordance of blood and urine isolates in bacteremic patients was observed in 0.52% of catheters placed and 4.8% of catheters with bacteriuria.

Catheter-acquired UTI is a source for less than 3% of bacteremic episodes in critical care units, despite the almost universal use of catheters in these patients.

For residents with a chronic indwelling catheter (in situ more than 30 days), the prevalence of bacteriuria or funguria is 100%. The rate of acquisition of new organisms remains 3-7% per day, similar to that observed for short-term catheters.

More than 50% of episodes of fever in residents of long-term care facilities with chronic indwelling catheters have a presumed urinary source (an incidence of 0.69-1.1 per 100 catheterized patient days).

UTI in residents with chronic indwelling catheters is the most common source of bacteremia in long-term care facility residents. These residents have been reported to have up to 39 times more episodes of bacteremia from a presumed urinary source compared with residents without an indwelling catheter.

At autopsy, histologic evidence of acute pyelonephritis is present in 38% of residents with a chronic indwelling catheter and only 5% without a catheter. Histologic evidence for chronic pyelonephritis correlates with the duration of indwelling catheter use.

Chronic indwelling catheter replacement is accompanied by bacteremia in 3-4% of episodes, but negative clinical outcomes attributable to bacteriuria with catheter replacement have not been reported.

Mode of spread

Most patients have an endogenous source for organisms causing bacteriuria. Infection follows ascension of organisms in biofilm up the catheter, usually originating from colonizing flora of the periurethral area and, in women, the vagina.

Organisms colonizing urine drainage bags may be transmitted between catheterized patients on the hands of staff or through contaminated equipment, such as urine measuring devices. This is a presumed mechanism of spread in reported outbreaks of resistant organisms among catheterized patients in acute care facilities.

What pathogens are responsible for this disease?

Escherichia coli is the single organism most frequently isolated from catheter-acquired bacteriuria or symptomatic urinary infection, but a wide spectrum of other bacteria and yeast species also occur.

Organisms isolated from patients with catheter-acquired urinary infection are characterized by a high frequency of antimicrobial resistance, attributed to repeated prior exposures to health care interventions and antimicrobials.

The urine of catheterized patients is a frequent source for isolation of resistant organisms, such as vancomycin-resistant enterococci and extended spectrum β-lactamase producing E. coli or K. pneumoniae. Staphylococcus aureus, including methicillin-resistant S. aureus, are occasionally isolated but are relatively infrequent. Yeast species are frequently isolated; Candida albicans is most common.

How do these pathogens cause urinary tract infection?

Biofilm formation is the determinant of infection. Organism virulence factors are not a determinant of symptomatic UTI in patients with an indwelling catheter. The prevalence of E. coli virulence factors in bacteremic or nonbacteremic catheter-acquired infection is similar to that reported for strains isolated from other patients presenting with complicated UTI, and much less common than strains isolated from patients with acute uncomplicated UTI.

Urease producing organisms, such as P. mirabilis, P. stuartii, K. pneumoniae, and M. morganii, are more likely to be isolated from individuals with catheter-acquired UTI, perhaps because they are more competent for biofilm formation. P. mirabilis, in particular, may be associated with crystalline biofilms that cause bladder or renal stones and catheter obstruction.

What other clinical manifestations may help me to diagnose and manage catheter-acquired urinary tract infection?

When taking the patient's history, ask about recent urologic interventions.

During the physical examination, check for purulent discharge from around the catheter and, in men, tender or swollen epididymis or prostate.

How can catheter-acquired urinary tract infection be prevented?

Programs to limit catheter-acquired UTI should be part of the infection prevention and control program for all health care facilities.

Programs should include written guidelines for indications for catheter insertion, adequate numbers of appropriately trained staff, monitoring of staff adherence to recommended catheter practices, and monitoring of catheter use and the incidence and outcomes of catheter-acquired UTI.

The single most important intervention is to avoid use of an indwelling urinary catheter. A catheter should be inserted only when there are clear indications and, once inserted, be removed as soon as no longer indicated.

Use alternates to an indwelling catheter, such as condom drainage for men or intermittent catheterization, when possible.

Appropriate indications for indwelling urethral catheter use identified by the Healthcare Infection Control Practices Advisory Committee are limited to:

acute urinary retention or bladder outlet obstruction

accurate measurement of urine output in critically ill patients

selected perioperative use:

urologic/genitourinary surgery

prolonged duration of surgery

large volume infusions or diuretics during surgery

intraoperative monitoring of urine output

assist in healing open sacral or perineal wounds for selected incontinent patients

Periurethral cleaning with antiseptics or instillation of antiseptics into the drainage bag is not recommended.

There is no evidence to support silicone, rather than latex, catheters for the prevention of urinary infection.

Decreased obstruction with silicone is likely due to the larger lumen.

Silicone may be less irritating to the urethral mucosa.

Antimicrobial coated catheters and complex catheter systems have not been shown to decrease the incidence of symptomatic infection or, in most cases, bacteriuria and are not recommended for routine use.

Routine replacement of chronic indwelling catheters is not recommended.

Catheter replacement is recommended only if obstruction, catheter malfunction, or prior to antimicrobial therapy of symptomatic urinary infection.